This invention relates to calcium hypochlorite blends; particularly to blends of solid calcium hypochlorite in combination with an alkali salt form(s) of anti-scaling polymers, wherein the polymer(s) are present in an alkali salt form effective at reducing the hygroscopic characteristics of the solid polymer(s), and subsequent calcium hypochlorite blend. This invention also relates to a means of reducing the reactivity of solid calcium hypochlorite with the said polymer(s) by applying a coating of the polymer(s) to the solid calcium hypochlorite.
U.S. Pat. Nos. 5,112,521 and 5,004,549 disclose the blending of Phosphono-Butane-Tricarboxylic acid (PBTC) with calcium hypochlorite to produce a solid calcium hypochlorite blend that inhibits scale formation associated with the reconstitution and dispensing of the calcium hypochlorite solution.
U.S. Pat. No. 6,146,538, the contents of which are herein incorporated by reference, discloses the use of Polymaleic acid (PMA) and/or Polyepoxysuccinic acid (PESA) in an alkali salt form that is blended with calcium hypochlorite to reduce or eliminate scale formation associated with the reconstitution and dispensing of the calcium hypochlorite solution.
It is known that increased moisture, especially localized moisture, increases the rate of decomposition of calcium hypochlorite. During decomposition, oxygen is released, with chlorides and chlorates typically being the resulting byproducts. In the presence of sufficient moisture, exothermic reactions result, oxygen release increases, and a potential fire hazard is produced when fuel sources are available, e.g. cloth, hydrocarbons and the like.
PBTC disclosed in U.S. Pat. Nos. 5,112,521 and 5,004,549, when combined with calcium hypochlorite as an anti-scaling agent, can nevertheless compromise manufacturing safety and solid product stability, due to its inherent hygroscopic characteristics.
It has now been discovered that the alkali salt forms of PMA, PESA, and similar polymeric salts which are commonly employed as deposit control agents, can significantly reducing the hygroscopic characteristics of calcium hypochlorite when combined therewith, in addition to providing enhanced anti-scaling properties. It has been further discovered that a coating of these polymers or blends thereof significantly reduces the reactivity of the solid calcium hypochlorite blend.
Thus, a step forward in the art is realized via provision of a solid calcium hypochlorite combination which simultaneously exhibits anti-scaling properties and reduced hygroscopic and reactivity characteristics. Such a composition yields improvements in both manufacturing safety and product stability by reducing moisture adsorption and subsequent decomposition of the calcium hypochlorite, as well as improved safety by reducing the reactivity of the solid calcium hypochlorite.
U.S. Pat. No. 4,146,676 describes calcium hypochlorite particles coated with about 4 to 45 percent by weight of a low melting inorganic salt, e.g. aluminum sulfate hydrates, to reduce dusting during handling and to increase stability of calcium hypochlorite contacted with lighted cigarettes or reactive organic materials such as glycerine.
U.S. Pat. No. 4,965,016 describes a granular calcium hypochlorite composition comprising a particle of calcium hypochlorite, the surface of which has been covered with a double decomposition product of calcium hypochlorite and an alkali metal hydroxide. It was shown the granular strength and stability was enhanced.
None of the prior art describes addition of an alkali salt of an organic polymeric anti-scaling agent to provide improved deposit control, while reducing the stability and reactivity of the solid calcium hypochlorite.
The instant invention is directed toward a solid calcium hypochlorite product formulation and a method for its production, which product exhibits improved environmental stability and shelf-life while simultaneously inhibiting scale in dispensing equipment, as well as in and on feed equipment used for delivering a calcium hypochlorite solution to a water stream which is to be treated.
A solid calcium hypochlorite composition with improved hygroscopic and reactivity characteristics is formulated comprising hydrated calcium hypochlorite and an alkali salt of Polymaleic acid, Polyepoxysuccinic acid or mixtures thereof, having between 0.01 and 10% by weight of said alkali salts, an available chlorine concentration of at least 30% and water in the range of about 2% to about 20% by weight.
In a particularly preferred embodiment, the composition is a solid having greater than about 50% active Calcium Hypochlorite which exhibits anti-scaling characteristics and reduced hygroscopicity and reactivity.
The solid calcium hypochlorite may be coated and/or encapsulated with at least one polymeric alkali salt selected from within the group including polymaleate, polyacrylate, polyacrylamide, polycarboxylate, polymethacrylate, Phosphinopolycarboxylate, Carboxylate-Sulfonate copolymer, Maleic Anhydride copolymer, Polyepoxysuccinate, maleate-sulfonate copolymer, maleate-phosphonate copolymer, carboxylate-phosphonate copolymer, and/or mixtures thereof.
The alkali salt may be selected from at least one of the group including the sodium, potassium, lithium, calcium, or magnesium salts and mixtures thereof. Additionally, the polymeric alkali salt may be in a liquid, slurry, or solid form.
At some point in the manufacturing process the calcium hypochlorite may be formulated/treated with a deposit control agent including at least one alkali salt(s), e.g. sodium, potassium, lithium, calcium, magnesium and/or mixtures thereof, of polymaleic acid, polyexpoxysuccinic acid, maleic anhydride copolymer, phosphinopolycarboxylic acid, carboxylic-sulfonic acid copolymer, maleic-sulfonic acid copolymer, maleic-phosphonic acid copolymer, carboxylic-phosphonic acid copolymer, and/or mixtures thereof. The weight percent of deposit control agent is within the range of about 0.01% to about 10% of the final weight of the formulated calcium hypochlorite product.
These polymers and copolymers will exhibit similar hygroscopic characteristics in the desired salt forms while providing deposit control capability. Furthermore, all are hydrophilic and possess high thermal stability. Therefore they will reduce reactivity of the solid calcium hypochlorite product.
Accordingly, it is an objective of the instant invention to provide a solid calcium hypochlorite product and a method for its production, wherein the resultant product exhibits reduced hygroscopic characteristics thereby improving the manufacturing safety and shelf-life and anti-scaling properties of the solid product.
It is a further objective of the instant invention to provide a coated or encapsulated solid calcium hypochlorite product having reduced reactivity and anti-scaling properties.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.